Modular off-site construction is one of the methods adopted by the construction industry in a recent drive to modernise its operations and increase its productivity. Operations that were traditionally performed on-site are instead completed at an off-site factory, with finished modules then being transported on-site for installation. Operating across two locations in this way can provide numerous gains in speed, quality, and costs. However, it does mean that construction companies must now understand and manage a new and wider range of potential disruptions to their operations. This thesis is concerned with addressing disruptions that delay the delivery of modules to site. To identify operational disruptions and their corresponding disruption management strategies, an exploratory study was performed consisting of five case studies and an industrial workshop. An over-reliance on storing modules as a means of coping with disruptions was uncovered. Construction sites typically follow a fixed module installation sequence because of on-site installation constraints. As such, when delivery of a module is delayed, subsequent modules in the sequence must be stored until the delayed module arrives for installation. As the industry expands towards manufacturing larger projects at higher production rates, storage may become a less viable disruption management strategy given the lack of storage space, particularly in urban areas. To overcome these challenges, a novel disruption management strategy is proposed and evaluated: on-site installation flexibility. There are four types: vertical assignment flexibility, lateral assignment flexibility, vertical sequence flexibility, and lateral sequence flexibility. Each type relaxes one of the on-site installation constraints, thereby allowing completed modules to continue to be installed in the event of a module being disrupted. Several conclusions were drawn from studying on-site installation flexibility as a disruption management strategy. Implementation roadmaps developed during a workshop using an Impact Matrix Cross-Reference Multiplication Applied to a Classification analysis and Interpretive Structural Modelling revealed that implementing on-site installation flexibility requires coordination and many changes across a range of organisational functions. A Discrete Event Simulation model developed and applied to a case study showed that on-site installation flexibility can reduce installation delay and storage requirements. Furthermore, combining more than one type of on-site installation flexibility can significantly improve system performance. However, greater co-ordination effort would be required to control module installation operations. Finally, a Simulation-Based Optimisation model was formulated and applied to a second case study and showed that investing in a combination of on-site installation flexibilities in conjunction with other disruption management options can achieve cost savings. Hence, on-site installation flexibility was demonstrated to be a promising disruption management strategy for modular off-site construction systems.